PROJECT SUMMARY Nine percent of the population will experience a seizure at some point in their lifetime, but only a fraction of these patients will develop epilepsy, a disease of recurrent unprovoked seizures. Understanding why some patients have an increased propensity for seizures and how to reverse this tendency is essential. More than a third of patients with epilepsy fail pharmacological therapy. Also while effective at decreasing seizures, there is little evidence that these therapies have any effect on epileptogenesis. Moreover, current diagnostic modalities lack the spatial resolution and specificity to accurately identify and treat brain areas involved in epileptogenesis. Surgical treatments removing putative epileptic tissue can sometimes fail to produce seizure freedom and can result in impairment of brain function. Thus, while significant progress has been made in the treatment of epilepsy, limited knowledge regarding its pathogenesis has precluded the development of more sophisticated therapies. Mesial temporal lobe epilepsy (mTLE) is the most common form of epilepsy in adults, and is characterized by seizure activity and pathology within the medial temporal limbic regions, including the hippocampal formation. Pathological changes in mTLE are particularly prominent in the dentate gyrus, a critical node for controlling activity in the hippocampus, and one of only a two regions in the mammalian brain where new neurons are born during adulthood. These newborn dentate granule cells make connections to other neurons in the existing network, appear to be important for forming new memories, and undergo an number of anatomical changes in mTLE. However, the function of newborn neurons and their role in hippocampal function and epileptogenesis are not known. Studies in this grant will employ the use of novel deep two photon Ca2+ imaging techniques to explore how newborn dentate granule cells recruit inhibitory neurons to quiet activity in the hippocampus, and how seizures alter this process. These aims reflect my long-term career objectives to develop stem cell-based therapies designed to quiet excitability and reverse epileptogenesis, as well as to engineer cells that express optical reporters of neural activity in human epileptic patients. This mentored award will provide specific advanced training in neural stem cells, experimental epilepsy models, and in vivo two-photon microscopy. This training will be conducted under the direction of Dr. Fred Gage, a leader in neural stem cells and neurogenesis. Drs. Tuszynski, Iragui, and Barba will provide additional mentoring in translational neuroscience and epilepsy, and ensure that I remain on track for career advancement. Together we have formulated a detailed career development plan providing training through regular mentor meetings, carefully selected coursework, seminars, and hands-on research experience. The proposed research and career development plan will benefit greatly from the intellectually rich and collaborative environments at UCSD and the Salk Institute.